Ciphering system



July 9,1946. L M, Fons 2,403,681

CIPHEkING S YSTEM Filed Sept. 18, 1944 2 Sheets-Sheet 1 57 45 FIG. -I 1 Emmi-1112i :in ilj 131:0;

724M121 13mg mvem'on L0 U IS M. POTTS ATTORNEY i 6- v 1 M. POTTS 2,403,681

- CIPHERING SYSTEM I Fil s p 18 19 2 Sheets-Sheet 2 s21 INVENTOR .LOUIS M.-POTTS ATTORNEY Patented July 9, 1946 CIPHERING SYSTEM Louis M. Potts, Evanston, Ill., assignor to Teletype Corporation, Chicago, Ill., a corporation of Delaware Original application October 19, 1942, Serial No.

462,523. Divided and this application September 18, 1944, Serial No. 554,636

a 1 This invention pertains to printing telegraph systems and particularly to a system for the transmission and reception of secret telegraph messages.

This application is a division of copending application Serial No.'462,523, filed October 19, 1942. Secret signaling systems are desirable for naval,

3 Claims. (01. 17871) military and civil purposes wherein it is required that messages be rendered uninterceptible by persons unauthorized to receive them. The surreptitious interception of messages may be accomplished, for example, in the case of wire communication by tapping signal wires and in radio communication by means of receiving apparatuses tuned to the proper frequencies. 7

The primary object of the present invention is the provision of a reliable and practical telegraph circuit arrangement for rendering messages unintelligible to unauthorized persons.

Another object of the present invention is the provision of a ciphering system for telegraph messages including an electrical circuit system which is automatically conditioned either to encipher or decipher signals according to the direction of transmission. V

A further object of the invention is to provide a portable self-contained enciphering and deciphering unit that is easily and readily attachable and detachable to standard telegraph printing apparatus having transmitting and receiving facilities.

.In one form, the invention utilizes a receiving distributor by means of which a set of five receiving relays are conditioned upon the receipt of enciphered or deciphered'signals and a key' tape transmitter for providing key signals. The

key signals are combined with the signals provided by the receiving relay and produce resultant signals which are transmitted by means of a transmitter-distributor to a transmitting relay having a pair of associated transmitting contacts, only one of which is efiective for transmission at a time dependent on the direction of transmission.

A second form of the invention features the use of a double wound relay for enciphering and deciphering messages. One Winding of the relay is under the control of key signals and the other winding is under the control of either enciphered.

or original signals dependentupon the direction of transmission. In this instance, two distributors are provided, one for key signals and the other for either the original or enciphered signals.

the second form except that two separaterelays A third form of the invention closely resembles 2 are employed for transmitting purposes instead of a double wound relay.

In order to .encipher messages by the present system the elements of the original code combinations are combined'with the elements of code combinations provided by a key tape. In this arrangement, opposite conditions, that is, with one element of the original code combination marking and with the corresponding element of the key code combination spacing, produce a marking signal. Like condtions, however, that is, With-both elements marking or both elements spacing, produce spacing signals. This presumes, of course,'that each of theelements of the respective code combinations are related to each other. That is, the No. 1 element of the original code combination is combined with the No. 1 element of the key code combination, and so forth. To take a specific illustration, let it be assumed that it is desired to encipher the letter R. which in the Baudot code is composed consecutively of spacing, marking, spacing, marking, and spacing conditions. Let it be further assumed thatthe key tape with which the particu lar enciphering operation is to be performed 00-. cupies a position whereat itis conditioned for producing the letter Y combination which in theBaudot code is composed consecutively of Original signal s M s Key signal Y" M S M Enciphered signal letters" M M M It is understood that both the transmitting and receiving end of a telegraph line will be equipped with identical key tapes, which'during message transmission will occupy identical positions. The key tapes are advanced during transmission to continuously modify the key signal,

but both tapes occupy the same corresponding position at all times. A station which receives enciphered signals is thus enabled to decipher the I unintelligible signals transmitted over the telebe combined with the letters combination to decipher the enciphered signals to thereby reproe duce the original signal R as clearly shown in the following chart:

The invention may be more readily understood from the following detailed description and the drawings wherein,

Fig. 1 is a circuit diagram of the main embodiment of the invention;

Fig. 2 is a circuit diagram of a second form of the invention;

Fig. 3 is a circuit diagram of a third form of the invention; and

Figs. 4 and 5 are schematic views showing methods of interconnecting communicating stations.

Referring now to Fig. 1, the first form of the invention will be described in detail. In order to facilitate the description of the first embodiment of the invention, it will be assumed that a local station comprising unit i l desires to communicate with an outlying station over a loop circuit indicated at 12. In order to make a local record and check the operation of enciphered signals, a check printer I3 is provided which, by means of the plug and jack arrangement shown at 14, may be readily plugged into the loop circuit. Similar plug and jack connections for the station unit I l and the loop l2 are shown respectively at l5 and 15. The apparatus is provided with a manually-operable switch shown generally at IT, by means of i which the local station unit ll may be conditioned to transmit and receive either regular telegraph messages or enciphered messages. When it is desired to transmit or receive enciphered messages, switch I1 is operated to its upper or coding position, and conversely, when it is desired to transmit or receive regular telegraph messages, switch i1 is positioned to its lower position.

The circuit for .the local station unit H may be traced as follows: From battery l8 through the winding of receiving relay 22, over conductors 23 and 24, through contact tongue 25 of transmitting relay 2%, over conductors 21 and 28, through tongue 29 of switch l1, over conductor 31, through the station H, back over the conductor through tongue 33 of switch l1, and over conductor 34 to ground:

When local station unit If commences to transmit, the just-described circuit is interrupted and relay 22 is de-energized due to the transmission of the start or no current signal. When this occurs, the following circuit is established: From battery 35, over tongue 36 of direction relay 31, over conductor 33, through the winding of direction relay 39, over conductor 4|, through contact tongue 42 of receiving relay 22 (now deenergized), over conductor 43, over conductor 46, through the winding of start magnet 44 associated with receiving distributor 45, over con ductor il, and through contact 49 of make-before-break contact 48 to ground. The operation of start magnet 44 releases distributor for the reception of a signal code combination from station unit II at this time, and the distributor is brought to rest upon the impression of the stop or marking impulse upon magnet 44, which follows after every five-unit code combination. In the rest position of the distributor 45, a circuit is made for relay 5| which may be traced as follows: From battery 52, through the winding of relay 5i, over conductor 53, through segment 54 of the distributor, over the brushes 55, and through conducting ring 56 to ground. As brush moves off segment 54, the circuit for relay 55 is broken, whereupon armature 51 is released to open contact 49 to break the energizing circuit of start magnet 44, and moreover, direction relay 39 becomes locked up over the following circuit: From. battery 35, through contact tongue 35 of direction relay 3?, over conductor 33, through the winding of direction relay 39 (now energized), through its associated contact tongue 6|, over conductors 52 and 63,

through contact tongue 51 of relay 5| (now deenergized) and through contact 58 of the makebefore-break contact 48 to ground.

With direction relay 39 thus energized, its contact tongue 84 is held attracted so that transmitting contact 25 or transmitting relay is shunted out of circuit ever conductors 21 and 66 inasmuch as at tl is time it is desired to transmit from station l I to the remote station over the transmitting contact iil. This prevents the operation of contact 25 from interfering with the operation of the circuit under the first assumed condition with station H transmitting, At this time, the direction relay 39 also holds its associated tongue E8 in its attracted position so that contact tongue 13 associated with relay H is shunted out of circult and rendered inefiective, in view of the fact that it is necessary at this time that outgoing signals which are transmitted through the relay "H do not interfere with the operation of the circuit. This shunting circuit is as follows: From contact tongue 58, over conductor I2, through contact tongue 13 (if it should be attracted by its associated receiving relay 1 I) over conductor 14, over conductor 15, and over conductor '16 back to the contact tongue 68.

The operation of direction relay 39 further results in the attraction of its contact tongue 1'! to deprive direction relay 3'! of battery so that the local station unit Il may assume complete control of the circuit, and therefore signals from a remote station at this time will be ineffectual to seize control of the circuit. After every revolution of the distributor 45, brushes 55 return to their rest position whereat the previously described circuit is made to the relay 5| which by its operation attracts its tongue 51 to break the locking circuit to relay as to return the circuit to normal in preparation for subsequent operations.

As the original signals are received from station unit H by the local relay 22, contact tongue 3! is operable to make and break the following circuit, according to whether markin or spacing impulses are being transmitted: From battery 82 through the windings of the receiving relays 83' (receiving marking signals), over conductors 84 to ,88, dependent upon the code combination being transmitted, through associated segments 89, over brushes 9|, over the solid conducting ring 92, over conductors 93 and T2, through contact tongue '68 (now atwa s;

16 and 95 and through the contact tongue 8| of local receiving relay 22 (when marking signalsare being received and receiving relay 22 is accordingly energized) to ground.

. When a particular receiving relay 83 becomes energized over the just-described circuit, it is locked up as follows: From battery 82, through the winding of a particular relay 83, over its contact tongue 96, over conductor 91, and through contact 98 of locking relay 99 to ground. Prior to the reception of each signal code combination, locking relay 99 is momentarily energized to break previous locking circuits, which may have been completed over the following circuit: From battery IOI, through the winding of locking relay 99, over conductor I02, through segment I03 of the distributor 45, over the brushes 55, and through the solid conducting ring 56 to ground.

In order to effect the enciphering of outgoing messages and the deciphering of incoming messages, there, is provided in the ciphering system of the present invention, a key tape transmitter indicated generally at III which utilizes a key tape H2. It will be understood, of course, that each station will be provided with identical key tapes which occupy identical positions during communicating operations.

Theonly prerequisite is that at any particular instant or communicating operation, the key tapes at the interconnected stations be identical, because the key tapes may be different at diiferent times or operating periods. Enciphered or deciphered signals dependent upon the direction of transmission, are delivered to the transmitting relay 26 through the instrumentality of a transmitting distributor II3.

Shortly after the operation of the receiving distributor 45,'segment II4 thereof is traversed by the brush 55 and a circuit is completed to the start magnet II5 of the transmitting distributor I I3 from ground, through solid conducting'ring 56, over brushes 55, through segment I I4, through the winding of start magnet II5, and through battery I I0 to ground, to place transmitting distributor H3 in operation. It' is, therefore, observable that the transmitting distributor II 3 lags behind receiving distributor 45, the purpose of which is to provide an overlap arrangement to secure the proper margin of operating time for the ciphering operation, to insure that the receiving relays 83 and the key tape II2 are properly conditioned for operation at the required time interval.

As the receiving relays 83 respond to signals,

associated tongues or armatures I2I are either attracted or not, depending upon whether a marking or spacing signal is impressed on storing relays 83. The circuit for the upper three receiving relays 83 is so designed with respect to the upper three tape feelers I22 of key tape I I 2 that a marking signal will be produced when the tongues I2I of the relays 83 are conditioned to a position opposite to that of the corresponding tape feelers I22. On the other hand, when a particular contact tongue I2I moves to a position similar to the position assumed by its associated tape feeler I22, the circuit is conditioned .to produce a spacing signal; therefore, when contact tongue I2I and tape feelers I22 are both marking or both spacing, a'spacing signal will be sent. The circuits for marking signals may be traced as follows: From battery I I6, through the winding 'of transmitting relay 26, over concuit for either of the overlap relays ductor I 23, through the solid conducting ring I24 of the transmitter distributor II 3, through brushes I56 and segments 1, over a particular conductor I55 conditioned for operation through a tape feeler contact tongue I22', over either the conductor I26 or I21, and through a contact tongue I 2I to ground.

In order to provide for the previously men'- tioned overlap condition, the lower two receiving relays 83 will cooperate by means of their tongues I2I with the lower two tape feeler contact tongues I22 in a slightly different manner. When either of the lower two tape feeler contact tongues I 22 move to their lower, or marking position, upon the sensing of a perforation in the key type, a circuit is completed upon the operation'of overlap control relay I4I. Only the operation of the lowermost overlap relay I3I will be described. The circuit is as follows: From battery I32, through the winding of relax I3I, over conductor I42, through feeler contact I22, over conductor I44, through contact tongue I of overlap control relay I4I (when operated) to ground. When contact tongue I45 is attracted by overlap control relay I4I,' as will be later explained, make-before-break contact I46 will be operated to break a previous locking cir- I3I if they have been previously energized in a preceding signal code combination. This locking circuit extends from battery I32, through the Winding of relay I3I, over contact tongue I5I, conductor I52, and through make-before-break contact M5 to ground. It is thus apparent that if in the immediately preceding signal combination lower tape feelers I2'2 were in their spacing positions their associated overlap relays I3I would not have been operated, and. consequently, although tongue I45 will operate; it will not unlock any circuit inasmuch as there was no circuit previously prepared for the relays I3I. The operation of tongue I45 also performs the function of providing ground over conductor I44, through the windings of relay I3I if they are prepared by a marking condition of feelers I22 for a marking operation in the next position of key tape II2.

Overlap control relay MI is momentarily energized at each cycle of operation of distributor 45 prior to the transmission of the signal code combination over the following circuit: From battery I41, through the winding of relay I4I, over conductor I53, throughvthe contact segment I 54 of distributor 45, over conductor ring 56, to ground. In accordance with the combined positions of tongues I33 of overlap relays I3I and the tongues I2I of the lower two receiving relays 83, ground I may be furnished when marking conditions occur over either conductor I34 or I35, through the contact tongue I33, over conductor I55, through brush I 56, over the solid conducting ring I24 and over conductor I23, through the winding of transmitting relay 26 to battery I I6.

During each revolution of distributor 45, step mitted since overlap relays l3 rare locked up and retain the fourth and fifth elements of the signal code of the previous code combination when these elements are conditioned for marking impulses by the key tape I 12. When spacing signals are provided in the fourth and fifth elements of a key code combination by the key tape, tongues I33 of the overlap relays [3! will remain unattracted in spacing position.

As relay 2%) is affected by the enciphered signals, its contact tongue 6! is opened and closed according to the signals that are being transmitted to the remote station. The signals transmitted, are, of course, start-stop code signals.

The key signals (that is, the signals controlled by the key tape) are provided only for the code impulses and not for the start and stop impulses, the latter impulses being invariable and are supplied independently of the key tape by the di tributor segments H8 and N9 of the distributor H3. Since the normal stop condition of the line is marking, the stop impulse impressed on the line is controlled by the energized relay 26, whose circuit under this condition extends from battery H8, through the winding of relay 26, over con-- ductor I23, over solid ring I24, over brushes I56, and through stop segment MB to ground. Then upon initiation of transmission, when start magnet I I is energized and brushes I56 are caused to traverse the segments; the traversal oi brushes E56 over the start segment H9 will produce a no current condition on the line, since no battery is connected to the start segment H9. Hence, the circuit previously traced for relay 2%; will be broken, and relay 2% will become de-energized to release its armatures 6i and 25 to transmit start impulses, either to the line 12 or to the local unit H, depending upon the short circuit condition of said contacts 61 and 25, as previously described. This causes the opening and closing of 100p circuit l2 to operate a printer at the remote station. This circuit is traceable as follows: From ground, through transmitting tongue 61, over conductor I59, through the winding of relay H, over conductor I51, through the lower switch tongue 158 of switch ll, over conductor I58, through the plug and jack connection it, through the outgoing part of the loop to the remote station, back through the plug connection [6, through the plug connection [4 of the check printer 13, over conductor ltl, through switch tongue Hill of switch i1, and over conductor 32 tobattery I49. The encip-hered signals which will be printed by the check printer l3 are also transmitted over the outgoing loop circuit ['2 to the remote station either directly or through a central telegraph office or exchange. The system having now been described with respect to transmission of outgoing enciphered signals, a description will now be given wherein enciphered signals are received over the loop circuit l2 from a remote station and are deciphered by the ciphering system.

Since the normal condition of the remote station in its idle or rest position is marking (current on the line conductors), the relay II will be energized over the previously described circuit including conductors I57 and 62. Thus, when, code signals are received from the remote station, the start impulse will cause relay H to become de-energized. When this occurs, contact tongue I93 of receiving relay "H is released and the following circuit is completed: From battery 35, through contact tongue 11 of relay 39, over conductor ltd, through the winding of direction relay 31, over conductor I55, through contact tongue I63 of receiving relay 1| (now de-energized) over conductor 46, through the winding of start magnet 44 of the receiving distributor 45, over conductor 41, through the make-beforebreak contact 48 associated with relay 5!, to ground. Therefore, at this time, the distributor 45 is released for a cycle of operation through the operation of start magnet M and the direction relay H is energized and becomes locked up over the following circuit after brush 55 [passes off of segment 5:! to cause the de-energi'zation of relay 5!: From battery 35, through tongue 11 of direction relay 39, over conductor Iii-1, through the winding of direction relay 31, through contact tongue [l2 (now attracted), over conductors 62 and '63, through tongue 51 of locking relay 5| and through make-before-break contact 48 to ground. The attraction of tongue 35 by the direction relay 31 breaks the possible operating circuit for direction relay 39 so that again it is apparent that the station which first seizes control of the system prevents the other station from operating during a signal code combination.

When direction relay 31 operates, contact tongue H3 associated therewith is attracted so that contact tongue 61 of transmitting relay 26 is short-circuited in order to suppress interference by this contact with the circuit at this time. This circuit is as follows: From ground, through contact tongue I13 of relay 3?, over conductors H4 and 59, through contact tongue 61 to ground. It is thus obvious that when the contact tongue 61 operates inasmuch as it is directly grounded, it will not cause the repetition of signals at this time.

Operation of direction relay 3? further causes the attraction of its associated contact tongue H5, and ground for the storing relays is furnished over the following circuit: From battery 82 to a particular receiving relay 83, over one of the conductors B l to 38, through its associated contact segment 89, over brushes 9!, through the solid conducting ring 92, over conductor 93, throughcontact tongue 13 of relay H, overcondu'ctor "i -i, through contact tongue H5 (now attracted) of direction relay 31, to ground.

Distributors 45 and H3 will act in the same manner aswhen signals were being sent out or transmitted, to now decipher the incoming signals to cause the deciphered signals to be repeated by the transmitting relay 25. It will be remembered that contact tongue 61' of transmitting relay 26 is now short-circuit-ed and rendered ineffective for transmission. However, at this time, transmitting contact tongue 25 is conditioned for operation and may make and break the circuit to the local station unit H to enable the local printer to print the incoming signals in their original or deciphere'd condition. This circuit is as follows: From battery 18, through the winding of local receiving relay over conductor 23, over conductor 24, through contact tongue 25 (when attracted) of transmitting relay 25, over conductor 27, over conductor 23, through upper contact 29 of switch ll, over conductor til, through the local station unit ll, over conductor 32, through tongue 33 of switch I], and over conductor M, to ground. The circuit shown in Fig. 1 therefore provides a ciphering system in which messages may be either enciphered or deciphered dependent upon the direction of transmission.

Another form of the invention about to be described is shown Fig. 2. The circuit shown in Fig, 2 resembles the circuit shown in F151.

9 Particularly, in. this form of the invention there is provided no..overlap*feature,and a double wound transmitting relay 205 is employed instead of a singlewound transmitting relay 26. The circuit for Fig. 2, therefore, will only be described with respect to the portions wherein it varies from the disclosure of Fig. 1.

In the modification, a distributor 20! and a distributor 202 are "driven in synchronism upon the same rotary shaft, and at a speed suitable for the speed of transmission used. When start magnet 263 receives the start or no-current impulse at the commencement of transmission, the distributors are released for operation, and both brush arms now move together. Storing relays 204 will be conditioned in the manner described in connection with relays 33 of Fig. 1 to energize the left-hand winding of double wound transmitting relay 205 when marking conditions occur, over the following circuit: From battery 200, through the left-hand winding of relay 255, over conductor 206, through the conducting ring 201, over brush 209, through a particular segment 208, over a particular conductor 2!! now conditioned, through a particular contact tongue 2! 2 to ground. As a particular storing relay 204 becomes operative, it is locked up over the following circuit: From battery I99, over conductor 2!3, through the winding of a particular receiving relay 204, through contact tongue 2! 5now attracted, over conductor 2i6, and through contact tongue 2!! (when released) of relay 2|8 to ground. In the rest position of the distributor 20!, preceding each signal code combination, relay 2!8 is energized to attract its contact 2 I! and thus break any locking circuit which may have been previously established in the immediately preceding signal code combination. This circuit is as follows: From battery 2|0, through the winding of relay 2l8, over conductor 2l0, through segment 220 of distributor 20! over brush 209, through segment 22!,'to ground.

In synchronism with the operation of the storing relays 20s to control the left-hand winding of the double wound transmitting relay 225, key signals are furnished for control of the righthand winding of said double wound transmitting relay through the instrumentality of a key tape 222. Prior to the transmission of signal code combinations under the control of the key tape transmitter during each cycle of operation, tape stepping magnet 223 is operated, to step the tape to a new position, over the following circuit:

From battery I98, through the stepping magnet 223, through segment 224 of distributor 20!, over the brushes !91 and through the segment I96 to ground. r

The circuit for the right-hand winding of re lay 205 is as follows: From battery, through the right-hand winding of relay 205, over conductor 221, through solid conducting ring 228 of dis- 7 tributor 262, over the particular segment 229 conditioned, over a conductor 23!, through a'tape feeler contact lever 232, through the lower-or marking contact I95, and over the conductor 233 to ground. When signals are being transmitted to a remote station, transmitting contact tongue 234 is rendered effectiveas hereinbefore described in connection with contact tongue 6'! of Fig. 1, and transmitting contact tongue 235 is rendered ineffective by the short circuit including conductors 327'and 366 and contact 364. On the other hand, when signals are being received from a remote station, contact tongue 234 is short-circuited 10 and contact tongue 235 is rendered efiective for transmission.

When opposite conditions exist in the windings of the double wound transmitting relay 205, that is, with one winding conditioned for marking signals and the other winding conditioned for spacing signals, the relay will become unbalanced and its transmitting tongues 234 and 235 attracted. In other words, the two windings of double wound relay 205 are wound reversely, and thus have the effect of neutralizing each other when current vis present in bothwindings so that a condition of current in both windings is the same as current in neither winding, and in both cases the armatures 234 and 235 willbe released. On the other hand, .current in one winding and no current in the other Winding will have the effect of attracting both armatures 234 and 235, but only one armature will be effective for transmitting signals, since the circuit including the other armature will have been short-circuited. The circuit in Fig. 2 is in other respects similar to the circuit shown in Fig. 1, and it is therefore deemed unnecessary to describe again the circuit in detail.

Another form of the invention is shown in Fig. 3 which is similar to that shown in Fig. 2 except that instead of the employment of a singledouble wound transmitting relay, as relay 205, there are provided two separate transmitting relays and 252 operable by the identical circuit shown in Fig. 2. In the drawings, conductor 356 is the same as conductor !50 of Fig. 1, and conductors 321, 366,- and 328 are respectively the equivalent of conductors 2'1, 65, and 28 of Fig. 1..

'Relay 25! is operable either by enciphered or original signals to control its transmitting contacts 253 and 254. When the local station unit 255 is transmitting'enciphered signals over loop circuit 256 to a remote station, contact 253 is efiective and contact 254 is shunted out of the circuit due to the operation of the direction sending relay 25! which attracts its contact tongue 364. On the other hand, when incoming. signals are 'being received from the distant station contact 253 is short-circuited due to the closure of contact 258 upon the operation of the direction sending relay 259. At this time the direction relay 25'! is unoperated and armature364 is released to render transmitting contact 235 eifective.

It has already been explained that the ciphering system herein employed is predicatedupon the combination of key signals provided by a key tape with either original or enciphered signals. Under opposite operating conditions. that is, with one element of the code, provided by the key signals, marking, and a corresponding element of the code, provided by an enciphered or original signal, spacing, produces a marking condition of the signaling line. Like conditions, however; that is, with both elements of the code marking or both elements of the code spacing, produce spacing conditions of the signaling line. Referring again to the circuit shown in Fig. 3, it can be seen that according to the provision of key signals for the relay 252 contact tongue 26! will be operated, and it is apparent that ground'may be carried over either conductor 262 or 263 to the contact tongue 253 of relay 25! when opposite conditions exist. As contact 253 moves back and forth, it makes and breaks the circuit to the remote station over the loop circuit 256 thereby to transmit enciphered signals to the remote station. However, when incoming signals are received from the remote station over line 256, receiving relay 25] receives signals in their enciphered condition, and its associated contact 254 is adapted to cooperate with contact 25 5 to make and break the circuit to the local printer 255. At this time contact tongue 364 of direction relay Z5! is open and consequently in this direction of transmission, conductors 32! and 3% do not provide a shunt circuit. Conductor 2H now receives battery through the winding of relay 212, over the conductor 21!, through the conductor providing battery for transmitting contact 25 which may be extended over either conductor 212 or 213. Therefore, contact tongues 254 and 25 will operate together to make and break the local circuit to the. printer 255 according to signaling conditions.

loop circuit at said. stations isv provided. As previously described, the loop circuit of the system shown in Fig. 1 extends from ground, through contact 51, over conductor I58, through the winding of relay H, over conductor I51, through switch ll, over line loop l2 to the distant station and returning again through the switch l1, and then over conductor I52 and through battery I48 to ground. Itmay be desirable to provide battery from the distant station, so, to accomplish this result the conductor I62 and the ground lead from contact 61 have been shown as connected to a connector block 49 I. On any telegraph line, batteryis usually supplied at one end of the line and ground at the other, and the installer has specifications which, instruct him to strap certain terminals together. By means of the present invention, it is only necessary to show different strapping on the connector block to indicate the different types of circuit. In Fig. 5, the. outlying stations are indicated as connected throughan exchange. 402.

It is to be understood that various changes: and modifications may be made in the present invention without departing from the. spirit andscope thereof.

What is claimed is:

1. In a repeater system, a double wound relay, two line sections, one of the windings of said relay associated with one line section and the other winding associated with the other line section, signal repeating means controlled by said relay, switching means to condition the circuit for repeating in one direction or the other, and means operative upon initiation of a signal in one line section to disconnect the winding associated, with the other line section.

2. In a telegraph system, a double wound relay, two line sections, one of said windings associated with one line section and the other winding associated with the other line section, a repeater controlled by said relay and adapted to repeat signals from one line section to another line section, switching means to condition the circuit for repeating in. one direction or the other, means to control the operation of the switching means according to the spacing or marking nature of the current on one of the line sections when a signal is initiated, and means operative upon initiation of a signal in one line section to disconnect the winding associated with the other line section.

3. In a repeater system, a first station, a second station, a circuit connecting said stations, double wound relay means to transmit information in both directions over the circuit, one of the windings of said relay means associated with one line section and the other winding associated with the other line section, automatic means comprising a pair of instrumentalities at each station, one responsive to an. initial signal from said first station and the other responsive to an initial signal from said second station to alter the transmitting means at each station variably at intervals according to which instrumentality receives the initial signal, and means operative upon initiation of a signal in one line section to disconnect the winding associated with the other line section.

' LOUIS M. POTTS. 

